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Process for Converting Alkaline-Earth Metal Chlorides to Tungstates and Molybdates and Applications Thereof
Inactive Publication Date: 2010-12-02
COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES +1
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[0042]It is thus possible to extract the alkaline-earth metal from the medium in which it is found without necessarily modifying the qualitative, or even quantitative, composition of the solvent of this medium, which is very substantial in the context of the reprocessing of a spent nuclear fuel where it is highly desirable to be able to recycle the solvent considering the very large volumes of solvent used.
[0049]The use of the extraction process according to the invention within the context of the reprocessing of a spent nuclear fuel in molten chloride media has proved to exhibit many advantages.
Problems solved by technology
Its processing via a vitrification of the type of that used for processing final high-level waste resulting from hydrometallurgical processes for reprocessing spent nuclear fuels such as the PUREX process, cannot be envisaged due to its high chlorine content (≈60% by weight of the waste).
Specifically, since chlorine can only be incorporated within a silicate-based vitreous matrix up to 1 to 2 wt %, the vitrification of such a flux would make it necessary to dilute it at least 30 times, which would result in a completely unacceptable volume of high-level waste.
Method used
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example 1
Conversion of SrCl2 to SrWO4 in the Absence of any Other Chloride
[0064]In an aluminacrucible, the following were mixed at ambient temperature (20-25° C.): 1 g of SrCl2, having a purity greater than 99%, and 9 g of an LiCl / KCl eutectic, formed from 4.005 g of LiCl and from 4.995 g of KCl; then, still at ambient temperature, 2.0567 g of K2WO4 were added to the mixture thus obtained.
[0065]The crucible was introduced into a quartz tube that was sealed and that was heated at 500° C. at a rate of around 5° C. per minute. The tube was kept at 500° C. for 5 hours, then it was cooled at a rate of around 2° C. per minute until a temperature of 300° C. was reached. The contents of the crucible was then quenched in air.
[0066]A solid was thus recovered, which was submerged in ultrapure water at high temperature (25° C. or 100° C.) in order to make the SrCl2 that had not reacted pass into solution, then the assembly was filtered over a Büchner funnel, using a filter with a cut-off threshold of 0...
example 2
Conversion of BaCl2 to BaWO4 in the Absence of any Other Chloride
[0069]The same procedure as that described in Example 1 above was followed, except that 1 g of BaCl2 (instead of the gram of SrCl2) was dissolved in the eutectic and that 1.5657 g of K2WO4 was used.
[0070]The X-raydiffraction pattern of the powder thus obtained is represented in FIG. 2. This diffraction pattern shows a good agreement between the peaks recorded and those of the card calculated for BaWO4 (00-043-0646 (*)), proving that the BaCl2 initially mixed with the eutectic solvent was indeed converted to BaWO4.
[0071]The yield of the reaction, determined by weighing the BaWO4 and comparing the result of the weighing with the theoretical mass corresponding to 100% reaction, is greater than 90%.
example 3
Conversion of SrCl2 to SrWO4 in the Presence of RbCl and CsCl
[0072]The same procedure as that described in Example 1 above was followed except that 1 g of a mixture of SrCl2, RbCl and CsCl (1 / 0.5 / 0.5 w / w) was dissolved in the eutectic instead of the gram of SrCl2.
[0073]The X-raydiffraction pattern of the powder thus obtained is represented in FIG. 3.
[0074]This diffraction pattern is almost identical to that represented in FIG. 1, which proves, on the one hand, that only the SrCl2 was converted to tungstate and, on the other hand, that the presence of the two alkali metal chlorides in the reaction medium had no influence on this conversion.
[0075]The yield of the reaction (determined as in Example 1) is greater than 90%.
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Abstract
The invention relates to a process for converting an alkaline-earth metalchloride to at least one salt chosen from the tungstates and molybdates of this metal, which comprises the reaction of the alkaline-earth metalchloride with at least one precursor of tungsten or of molybdenum chosen from tungsten oxides, molybdenum oxides, tungstates and molybdates, this reaction being carried out in a solvent constituted by KCl or by an LiCl / KCl mixture and at a temperature at least equal to the melting point of this solvent.Applications: synthesis of alkaline-earth metal tungstates and molybdates, extraction of alkaline-earth metals from media in which they are found in the form of chlorides, recovery of alkaline-earth fission products from a salt flux in the context of the reprocessing of a spent nuclear fuel in molten chloride media, etc.
Description
TECHNICAL FIELD[0001]The present invention relates to a process that makes it possible to convert alkaline-earth metal chlorides to tungstates and molybdates, and also to the applications thereof.[0002]This process may, specifically, be used for synthesizing, starting from the corresponding chlorides, alkaline-earth metal tungstates and molybdates that can be used for research and industry such as, for example, calcium, magnesium, barium and strontium tungstates and molybdates.[0003]But it may also be used for extracting alkaline-earth metals from media in which they are found in the form of chlorides.[0004]Thus, the process according to the invention may especially be used in the reprocessing of spent nuclear fuels, for recovering the alkaline-earth fission products present in a molten chloride medium.[0005]It may also be used in the pollution control of chloride-rich effluents such as, for example, domestic or industrial wastewaters.PRIOR ART[0006]Essentially two types of pyrochem...
Claims
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